Wpf Validation

WPF Input Validation
presented by
Jonathan Birkholz

About Me
Blogs :
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GitHub : github.com/RookieOne
Email : rookieone@gmail.com

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If you know all this… then feel free to leave
How to do binding validation with:
Validation Rules
Exceptions
IDataErrorInfo
Enterprise Library - Validation Application Block
Markup Extensions

Objective
Not to tell you how to do input validation with WPF
Instead just show you a variety of methods available
In the end, you must decide which methods works best for you

Sample
App to create a list of party invitees
Rules for being an Invitee
Name is required
Age has to be greater than 18
Must have a valid email address

Using Validation Rules

Validation Rules
Validation Rules are the mechanism built into data binding with WPF

Binding – Markup Extension
Normally you see binding as
but that is just a binding markup extension.
We can also set a binding like this

Add Validation Rules to Binding
Binding needs to Validate on Data Error
Allows the setting of Validation Rules to Binding

What Validation Rules come with WPF

DataErrorValidationRule
ExceptionValidationRule

Custom Validation Rules
Just inherit from Validation Rule
And override Validate method …

Implement Validate and return ValidationResult
Fail
Pass
Validation Error Message

Required

Greater Than

Regular Expression

Displaying the Errors

Error Template
Creates the red border

Displaying Error Message
This is setting the error template we specified
This trigger sets the tooltip to the error message

Tooltip Conflicts
Now my normal tooltip shows
Now I loss my Error Message tooltip
This is due to how Property values are resolved … Styles, Triggers, local, etc

Using Exceptions

On source…
Throw exception

On binding…
Set ValidatesOnExceptions to True

Exception Messages
Hmm… not exactly the error message we would want…
And this message is lame…

Using IDataErrorinfo

Implement

On base ViewModel

On Party Invitee View Model

On Binding
Validates On Data Errors

Works great right?
Not quite so perfect….
Bad input… no error

Solution
Make Age a string
Change Error Checking

And now…

Enterprise Library

Enterprise Library is
The Microsoft Enterprise Library is a collection of application blocks designed to assist developers with common enterprise development challenges
One of which is the Validation Block

You can get EntLib 4.1 here
http://msdn.microsoft.com/en-us/library/dd203099.aspx

Add Reference

Use Validation Attributes

Error Provider
Martin Bennedik @
http://www.bennedik.de/2007/04/wpf-integration-for-validation.html
Download WPF Validation project
Has the ErrorProvider control
The error provider recursively finds all the bindings down the Logical Tree and adds the Enterprise Validation Rule to the bindings

On View
Wrap bindings to validate with the Error Provider
Bindings can remain simple

In action
Not exactly the best out of the box messages…

Setting the Error Message

New and improved

Custom markup extension

Markup Extensions
The most common markup extensions used in WPF programming are those that support resource references (StaticResource and DynamicResource), and those that support data binding (Binding)
Static Resource
Dynamic Resource
Binding

Custom Markup Extensions
We can make our own markup extensions
Use attribute to specify markup extension return type
Inherit from MarkupExtension
Implement ProvideValue

Binding Decorator Base
Philip Sumi @
http://www.hardcodet.net/2008/04/wpf-custom-binding-class

Base Validation Binding

Required
Implementation
Xaml

Greater Than
Implementation
Xaml

Email
Implementation
Xaml

With Custom Markup Extensions

Conclusion
We covered how we can do WPF Input Validation with
Validation Rules
Exceptions
IDataErrorInfo
Enterprise Library Validation Block
Custom Markup Extensions

Questions
?

Git Hub Repository
http://github.com/RookieOne/WPF-Input-Validation
Has solution with projects and slide show
Offered as is

References
MSDN
http://msdn.microsoft.com/en-us/library/dd203099.aspx
Blogs and articles by
Josh Smith
Karl Shifflet
Martin Bennedik
Philip Sumi